Impacts of Extreme Temperature and Drought on Water Quality and Phytoplankton Biomass in Nanwan Reservoir (China)

Climate change has led to increasingly frequent and unpredictable droughts and high-temperature events, creating extreme conditions that profoundly impact the productivity of freshwater ecosystems. In this study, we evaluated the effects of extreme temperature and drought events on Nanwan Reservoir, a large, deep body of water in Xinyang, China, by assessing water quality and phytoplankton biomass. Field investigations were conducted during both high-temperature and drought (HTD) conditions in 2019 and normal-temperature and non-drought (NTND) conditions in 2020. HTD conditions significantly disrupted the thermocline and oxycline structures, leading to prolonged stratification during this period. Although phosphorus concentrations remained relatively stable across both periods, nitrogen levels were markedly lower during HTD events, indicating a possible shift in nutrient limitation from phosphorus to nitrogen. Additionally, a complex relationship between environmental variables and phytoplankton biomass was observed under HTD conditions. These findings advance our understanding of primary production responses to extreme weather events in Nanwan Reservoir, highlighting the importance of incorporating this knowledge into water resource management and ecological conservation strategies.